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Morning folks, help me settle a debate with my sister please...
She moved into a 1970's, steel framed house a few years ago and suffers terribly with condensation on her windows every morning. The current windows were installed shortly after she moved in and I'm not sure they're particularly good quality.
The house is a relatively large, open plan detached property with very poor insulation. The temperate drops like a stone overnight and struggles to rise to a comfortable level in the daytime.
I've tried to explain the whole Air Temp / Relative Humidity / Dew point thing but she's having none of it. She's gone as far as measuring the surface temperature of the windows which she states are well above dew point and she is concluding that the condensation is occurring because the windows are "faulty" rather than accepting the science behind why it occurs.
So could there be something else at play here? Is it possible for condensation to occur on window surfaces above dew point? If so, how?
I've told her she essentially needs to raise the surface temp of the window above dew point by either -
A) Heating the house more
B) Reducing the relative humidity
She's reluctant to turn the heating up given the house is so poorly insulated.
I good way to reduce humidity is to ensure adequate cooking and bathing extraction.
So many people don’t have or turn on either. First thing to check.
We live in a solid brick cottage with old sliding sash windows and have a dehumidifier running on low all winter. The amount of water I empty from it is incredible but the house warms up quickly when the heating is on.
I still have to vac the condensation from the windows every morning but it would be a lot worse than without the dehumidifier. It really makes a huge difference.
how is she accurately measuring the temperature of glass? thats not an easy thing to do accurately
I never suffered condensation but i highly insulated and improved the airtightness of my upstairs rooms and now the condensation occurs on the windows....
we are fitting new windows and a PIV
Thanks guys,
She's using a calibrated IR temp gun on the glass surface and a calibrated thermometer / hygrometer on the windowsill.
I suspect the air temp is even cooler right near the surface of the window compared to the windowsill which is obviously much more difficult to measure accurately. Inaccurate measurements = unexpected results.
I do love just how dull I've become these days 🙂
As above, get a dehumidifier. It will also make the heating system more effective.
Just to add - she's got a dehumidifier albeit I don't think it's running 24/7.
Those PIV units do look interesting. I haven't really given them a thought before.
Luckily our own house doesn't suffer with condensation as it's well insulated and ventilated. Funnily enough though our gas bill more expensive than theirs despite these things - our house is smaller too... with this in mind it does make me wonder just how much she's trying to heat it in the first place.
She’s using a calibrated IR temp gun on the glass surface
IR guns don't work well on reflective surfaces regardless of how calibrated they are!
The short story is that her glass is cold [probably because the glazing units are not that good ...... depends on the air gap] and the moisture is condensing on them. Which windows are affected?
Adding more heat to the entire house just to warm up the glass seems a bit extreme, even if it works! Is she happy with the house temperature? Dehumidifier seems to be a potential solution, [edit] but they don't work if they're not switched on.
I was/am in a similar situation in a Victorian house without double glazing or any form of insulation (renting).
Got one of these https://www.meacodehumidifiers.co.uk/products/meacodry-20l-arete-one-dehumidifier-white and ran it 24/7 for about a week. It sucked about 25l of water out of the air. It still goes on occasionally, mostly self-controlled, but it has changed the way the house feels, fresher and warmer.
We think the increase in RH was down to the really wet October/November and the house never really drying out due to lack of sun - of that makes sense.
A good way to reduce humidity is to ensure adequate cooking and bathing extraction.
So many people don’t have or turn on either. First thing to check.
I saw a landlord being interviewed in Newsnight a couple of years ago when mould in rented housing was first hitting the headlines. He was careful to acknowledge that there are some terrible owners of terrible buildings resulting in mould. But he was there to point out that in many, many cases the mould that was hitting the headlines was actually caused by tenants making no effort to extract moist air or ventilate the property. He had a huge issue with people complaining about mould in properties with wet clothes hanging over radiators, bathroom extractor fans turned off and windows permanently shut.
is she using the correct wavelength of IR thermometer.
IF i stand infront of a double glazed glass window and measure the temperature - i get a partial measurement of the reflected object.
IE - Me .
there are specific wavelengths of IR for measuring glass - these are generally not what your getting off the shelf in the DIY sheds. £XXXX
commonly people confuse the visible light spectrum pass through as the IR not being reflected.
Id be very warey of anyone giving measurements taken from glass with an IR thermometer.
The issue becomes very apparent when using an FLiR camera - you can see a perfect warm silhouette of the person behind the camera in a cold window.
every chance her windows above the dew point as shes actually measuring the temperature of an internal wall inadvertently.
That’s interesting about IR thermometers and glass. Initially I thought the reflective nature of the glass could be a problem so I stuck a very thin layer of masking tape over a section of the pane and took a measurement from that. It was always exactly the same reading as the measurement I took from the glass next to it.
She might well be right.
Albeit it might not be the windows rather how they have been installed.
The windows:
Are they thermally broken. Steel is a conductor of heat so if the outside of the frame connects directly to the inside it will conduct all of out warmth and get very cold. A thermal break is a bit of plastic sandwiche in the middle of the frame between the outside and the inside.
I would have thought to meet building regs in last few years it would have to be thermally broken.
The installation:
If they are thermally broken, have they been installed in the correct place over the cavity.
Is there anything filling the gap between the window frame and the wall. Often it is just air which will get cold. There should be un broken insulation with no gaps. If there are trims remove a bit of one on the outside and have a look. Similarly you can knock a little fillet of mortar from beneath the sill and look in.
What brand are the windows- open one and see if it says on any of the mechanisms or perhaps on a door.
There is also an interesting dynamic of a windows efficiency (u value) is based on the extruded frame before it is made into a window and so whilst the extrusion might have a good u value that doesn’t mean the window does. For example in metal windows there is often a bit of foam in between the inner and outer skin that is placed around the edges but this is removed for drainage at the bottom and air flow at the top if trickle vents. This compromises the thermal efficiency.
Your sister is incorrect. You are correct. Windows are almost always the coldest point in a buildings thermal envelope.
She needs to either increase the heat (insulate or use heating more) in the dwelling or dehumidify the air (Dehumidier, ventilation or MHVR).
Thermal performance of a 1970s steel frame building is probably crap. It's effectively dry lined, but with a massive cavity that will allow a ton of air to move about.
If she can't accept you're right, you'd best stand aside and watch her waster her energy on some kind of trade desciptions action.
Have you measured her indoor humidity?
It's worth spending a tenner on something like this..
It has a memory function so you can see the MAX RH you have 'achived' in the previous 24hrs.
Place it in the middle of the room, away from the windows...and away from your central heating thermostat, so you can cross reference temperature values.
How many people in the house? if theres 4 or 5 people and the windows are sealed TOO well, and closed all the time, you'll trap excess humidity inside the house... you still need ventilation, even on cold days, its worth cracking the windows for half an hour, depending on your humidity levels, and to get some clean fresh air!
PIV probably cheapest way to solve condensation issues but work on improving insulation next.
Not a cure but this ideal for removal
Fit a Drimaster PIV and 2 days later, no condensation.
@muddyjames - there’s a good chance the windows haven’t been installed correctly. The company that fitted them have removed and reinstalled them once already and are now coming back to do something else... let’s assume they are poorly installed / constructed, that wouldn’t mean condensation would occur on them despite being them being above dew point would it? Wouldn’t that just contribute to the poor insulation and therefore them being below dew point?
I personally wouldn’t trust the company to come back again without seeking advice from an independent specialist first. I don’t think she’s out of pocket yet but I can see it heading in that direction. You buy cheap you buy twice!
I don’t think these windows have any sort of kite mark or other markings on them…
There are 4 people and a dog in the house. Condensation is primarily in the bedrooms but also downstairs too. I think she dries multiple loads of washing in the house each week which will be a massive contribution to the problem.
She’s measuring the humidity and temps occasionally but it’s difficult to paint a picture as those readings are just a moment in time rather than a historical and meaningful log. I recently bought some SwitchBot meters which log the data throughout the day and have encouraged her to do the same.
My guess is that there's simply too much moisture in the house.
I think she dries multiple loads of washing in the house each week
This could be a massive problem if she just air dries stuff. A tumble drier would help massively.
(We've just changed from a vented drier to a condenser and the amount of water involved is pretty surprising)
If she is a bath lover then these are a big contributor also.
MrsSB has a bath most nights and we get condensation in our bedroom (en suite is open to the bathroom) even with the extractor running.
That said our DG units are old and nothing like as efficient/warm as modern units.
When you say she's had new windows.... Was that complete windows or just the DG units?
Complete new DG units were installed.
My guess is a combination of -
- House is far too cold due to poor insulation (low quality / poorly installed windows being a contributing factor)
- Unwillingness to turn the heating up a notch.
- RH too high
Until she accurately logs the temp / RH over a period of time we’re just working on educated assumptions.
Either way our disagreement was more about the science behind why it occurs vs her belief that it’s nothing to do with the dew point. She just has the simplistic view that the windows are faulty and the problem will go away if they get fixed.
I bought some of these a few weeks ago and they're great for seeing how temp and humidity are changing throughout the day - ThermoPro TP357
She just has the simplistic view that the windows are faulty and the problem will go away if they get fixed.
I'm struggling to see how a window can be 'faulty'!
@sharkbait as has been mentioned above it could well be the install not actually the window, there will almost certainly be a massive thermal bridge around the window reveals which will cool the inner metal part of the frame and also reveals regardless of how good the windows are. Insulating between frame and opening and also insulating all around the reveals in to the rear of the window frame would likely help. Some airtightness taping as well to control air ingress around frame.